PURPOSE: To provide an electromagnetic induction type fixing device capable of detecting a temperature with excellent responsiveness and accuracy and preventing the overrising of the temperature, so as not cause the burning of a transfer paper and smoking by detecting the Curie point of the magnetic material of a fixing roller and using the Curie point for the prevention of the overrising of the temperature, so that the fixing device can hardly affected by dispersion in parts, a set position for attaching, a set environment, etc.

CONSTITUTION: The electromagnetic induction type fixing device is provided with a primary coil part 4 interlinked with an external magnetic circuit part 3 for forming a magnetic loop on both end parts of the internal magnetic circuit part 2 of the fixing roller 1, a secondary coil part 5 formed outside the internal magnetic circuit part 2 and a power supply part for feeding power to the primary coil part 4. The Curie point of the magnetic material of which the internal magnetic circuit part 2 is made is set higher than a carry-over temp. at the time of keeping the fixing roller 1 at a fixable temp. and lower than the carry- over temp. when the fixing roller 1 has thermorunaway at the time of occurrence of abnormality and reaches a temp. requiring protection.